The Max Planck Institute for Biological Cybernetics is equipped with one of the strongest magnets (9.4 Tesla) for human Magnetic Resonance Imaging worldwide. These high field magnets facilitate morphological and functional neuroimaging at unprecedented spatial and temporal resolutions.

However, the high field strength comes at the cost of a short wavelength of the radiofrequency (RF) field that must be generated by the RF coils. As a result, interference effects cause severe inhomogeneities in the RF field and the magnetization across the human brain. This can lead to a highly impaired image quality if conventional RF coils and pulses are used for imaging.

This project aims on the development of RF transmission techniques and hardware in order to overcome this problem. In particular, I work on:

• Development of novel RF antennas that have the potential to create a more homogeneous RF field across the brain
• Simulation of the electromagnetic RF fields that are created across the human body
• Static superposition of RF fields that are emitted by an array of independent coils in order to create a markedly more uniform RF field in user defined regions deep inside the brain (Static parallel transmission / B1 shimming)
• Dynamic control of the single RF fields in concert with the spatial encoding gradients, which allows to actively control the buildup of transverse magnetization during the RF pulse (Dynamic parallel transmision / Transmit SENSE)

Parallel Transmission Techniques in MRI of the Human Brain at 9.4 Tesla

Patch Antenna Transmission

In this project, we developed a setup that combines a two-channel patch antenna for spin excitation with a 24-channel receive array for signal reception. The main advantages of this setup are a more uniform transmit field across the brain per se compared to conventional RF coils, simple usage without the need for calibration pre-scans as well as parallel signal reception with a high signal-to-noise ratio. Parallel transmission techniques can be utilized to a limited extend by using the two transmit channels of the antenna.

Static Parallel Transmission (B1 shimming)

For this technique, multiple independent coils are used for transmission. A proper superposition of the distinct transmit fields can be used to control the static RF pattern across the brain as desired, e.g. to achieve a high RF field homogeneity in localized areas. This is realized by introducing different constant phase and/or amplitude offsets to the current on single coil elements. Since the RF pattern is dependent on the shape of the subject’s head, it is necessary to acquire field maps of the single channels in rapid pre-scans.

Dynamic Parallel Transmission

In contrast to B1 shimming, the amplitudes and phases on multiple coil elements are independently and persistently varied during the RF pulse using dedicated hardware. Simultaneously, the spatial encoding gradients are controlled in order to create an arbitrary target magnetization. With a single RF coil, such pulses would normally be impractically long, but the use of multiple transmit coils allows for shortening them to reasonable lengths. Theoretically, this can be used for very high resolution imaging by exciting only a small field-of-view, as well as a further homogenization of the transverse magnetization pattern in localized brain areas.

Education

Since 05/2009

PhD student in the Graduate School of Neural & Behavioural Sciences / International Max Planck Research School at the High-Field Magnetic Resonance Center, MPI for Biological Cybernetics.

12/2007 – 01/2009

Diploma Thesis „Simulation of Electromagnetic Fields for the Development of NMR Coils“ at the High-Field Magnetic Resonance Center, MPI for Biological Cybernetics, Tübingen, Germany. Thesis supervisors: Dr. Rolf Pohmann, Prof. Dr. Wilhelm Kley.

2007

Student research project in scientific computing at the Faculty of Mathematics, University of Tübingen, Germany: "Numerical Integration of the Time-Dependent Schrödinger Equation through Fourier Basis and Strang-Splitting “

10/2002 – 05/2009

Diploma in Physics with focus on scientific computing at the University of Tübingen, Germany